Remove or replace XLSForms with `repeat` column on `entities` sheet

[lognaturel]

Blocked by XLSForm/pyxform#818

We will be changing the XLSForm spec for multiple Entity declarations per form definition and removing the repeat column entirely. The repeat column was never formally documented but we did use it for test forms. We should make sure that forms in the Drive and any other test forms we have around are updated to the new spec or removed.

[lognaturel]

Now that XLSForm/pyxform#818 is available on https://getodk.org/xlsform/, we can make this change.

[dbemke]

Tested with success!

[WKobus]

Tested with success